Interstellar dust and the sun
(Phys.org)—The space between stars is not empty. It contains copious but diffuse amounts of gas and dust; in fact about 5-10% of the total mass of our Milky Way galaxy is in interstellar gas. About 1% of the mass of this interstellar material, quite a lot in astronomical terms, is in the form of tiny dust grains made predominantly of silicates (sand too is made of silicates), though some grains are also composed of carbon and other elements. Dust grains are important. They block visible light while emitting infrared light, and thus help determine what astronomers can see while controlling much of the energy balance in the interstellar medium (ISM) by virtue of the absorption and subsequent re-emission at longer wavelengths of light from stars. Dust is also essential to the chemistry that takes place in the ISM because it provides gas molecules with a surface on which to react...